A few of the original 13 states started out as Protestant colonies but that was WAY before 1776. By then there were Catholics, Jews, Deists, etc. in America and the majority in some regions. The Quakers were big but that has very little to do with these guy's ideas about religion.
So our theocracy should reflect the founders beliefs? Many of them were Deists, who didn't even believe in the divinity of Jesus. Thomas Jefferson even wrote his own Bible with all the miracles and mention of Jesus's divinity removed.
Like most Conservatives they long for a time that never existed.